Description of problem:
After updating LVM:
- LVs using cache are not available. 
- pvdisplay, vgdisplay and lvdisplay no longer give any output.
- The following errors are displayed during boot. The boot process goes into emergency mode. 
Jan 29 10:49:59 hp9470m systemd[1]: Unit lvm2-pvscan@253:3.service entered failed state.
Jan 29 10:49:59 hp9470m systemd[1]: lvm2-pvscan@253:3.service failed.
Jan 29 10:50:00 hp9470m lvm[2718]: Internal error: LV vgSystem/lvVBoxCache has uknown feature flags 0.
Jan 29 10:50:00 hp9470m lvm[2718]: Could not format metadata for VG vgSystem.
Jan 29 10:50:00 hp9470m lvm[2718]: Update of lvmetad failed. This is a serious problem.
Jan 29 10:50:00 hp9470m lvm[2718]: It is strongly recommended that you restart lvmetad immediately.
Jan 29 10:50:00 hp9470m systemd[1]: lvm2-pvscan@253:0.service: main process exited, code=exited, status=5/NOTINSSTALLED
Jan 29 10:50:00 hp9470m systemd[1]: Failed to start LVM2 PV scan on device 253:0.

Downgrading LVM2 and device-mapper restores functionality.

Version-Release number of selected component (if applicable):
device-mapper.x86_64 - 1.02.93-1.fc21
device-mapper-event.x86_64 - 1.02.93-1.fc21
device-mapper-event-libs.x86_64 - 1.02.93-1.fc21
device-mapper-libs.x86_64 - 1.02.93-1.fc21
lvm2.x86_64 - 2.02.115-1.fc21
lvm2-libs.x86_64 - 2.02.115-1.fc21

How reproducible:
Always

Steps to Reproduce:
1. yum update
2. reboot


Actual results:
The above error appears. Some LVs are not available. Emergency mode is started.

Expected results:
The system should boot.

Additional info:
Severity set to urgent, as it causes boot failure.